1. Field of the Invention
The present invention relates to an air-cooled motor and, more particularly, to an air-cooled motor in which a through hole for passing a fluid is provided in a rotary shaft.
2. Description of the Prior Art
For driving the main shaft of a processing machine or the like, a motor in which a through hole is formed in the rotary shaft is widely used (for example, refer to Japanese Patent Application Laid-Open No. 10-146021). The motor of this type has a hole for passing a liquid or gas, which is formed so as to extend through the rotary shaft, and has a supply section using a rotary joint at the end of the shaft on the rear side of the motor in order to supply the liquid or gas into the through hole.
On the other hand, an air cooling type is often used to cool down the motor body. In this case, a structure commonly employed is that the exhaust direction of cooling air is set to the axial direction of the motor (the direction in which the rotary shaft extends), and the cooling fan is attached to the rear side of the motor. Therefore, the cooling air for cooling the motor body passes around the supply section in which the rotary joint is provided and reaches the cooling fan.
Consequently, if suction of outside air happens around the supply section, a loss occurs in suction force of the cooling fan so that the cooling efficiency of the motor body deteriorates. In order to prevent the deterioration, hitherto, a structure is generally employed such that the rotary joint is covered with a cylindrical member called a distance block and the cooling fan is attached to the rear end face of the cylindrical member.
In the conventional structure, however, since the rotary joint is covered with the cylindrical member, the rotary joint and its periphery cannot be seen from the outside. Therefore, if the rotary joint is broken, it is difficult to find such a breakage, and a leaked liquid or gas may be accumulated in the cylindrical member. When the cooling fan is attached to the motor side face so as not to interfere with the rotary joint, the cooling air is exhausted in the lateral direction and it causes a problem that a machine to which the exhaust air is blown is thermally displaced.